During semiconductor packaging, semiconductor chips or dice are usually mounted onto a substrate or carrier for processing. The semiconductor dice may be placed directly onto the surfaces of substrates, or such as in stacked dice configurations, they may be placed onto other dice. After attachment of the semiconductor die to the substrate or another die, the device is usually encapsulated in a downstream process.
Die bonding machines are used for picking up these semiconductor dice (which are typically cut from a wafer), and thereafter placing them onto substrates, carriers or other dice. Such die bonding machines have bondhead assemblies to hold and position die pick or die bonding tools that are used in these pick-and-place processes.
Due to the introduction of semiconductor dice that are becoming increasingly smaller in size, the demands on die bonding machines are becoming more exacting. Amongst other considerations, smaller and/or thinner dice are more prone to cracking, and require greater care in handling. Present die bonding systems are slowly becoming less capable of meeting these demands.
FIG. 1 is a cross-sectional side view of a conventional bondhead 110 used for die bonders. It generally comprises a bond body 102 that is carried by a support structure 104. The bond body 102 is drivable to move along a vertical axis by the raising or lowering of the support structure 104, and is mounted to the support structure 104 via an adjustable spring post 106 that further has a preload spring 108 between the adjustable spring post 106 and the bond body 102. The preload spring 108 biases the bond body 102 towards the support structure 104 when the bondhead 100 is in a standby position. Further, relative movement between the bond body 102 and the support structure 104 is guided by a cage bearing 110 movable along a shaft 112.
The bond body 102 holds a pick-and-place tool 114, which is operative to pick dice from a pick-up position and then place the dice and/or bond them at a placement position. The pick-and-place tool 114 is commonly in the form of a collet assembly. A vacuum outlet 116 connected to the pick-and-place tool 114 is used where the dice are to be picked using vacuum suction. In FIG. 1, a die 118 held by the pick-and-place tool 114 is being placed onto a substrate 120. The die 118 may be attached to the substrate 120 using adhesive or other means. A contact sensor 122 at an end of the bond body 102 is in contact with a portion of the support structure 104 during standby. The contact sensor 122 is disengaged from contact with the support structure 104 when the pick-and-place tool 114 is prevented from further downward movement as the support structure 104 is traveling downwards. The disengagement of the contact sensor 122 indicates that contact of the pick-and-place tool 114 has be made with a relatively fixed surface, and therefore of the die 118 with the substrate 120. Further lowering of the support structure 104 imparts a bond force to the die 118 by way of the force exerted by the preload spring 108.
In this conventional bondhead design, contact with a die is sensed using the contact sensor 122. The total moving mass comprised in the aforementioned bondhead is about 17 grams. A disadvantage of such a large floating mass is that a relatively higher impact force is imparted onto the die 118 from the pick-and-place tool 114. This may lead both to a shortened life of the place-and place tool 114 as well as occasional die crack. If the search velocity during die placement onto the substrate 120 is decreased in order to reduce the impact force, the downside is that the throughput of the machine is reduced substantially. Consistent performance is further limited by stiction in the cage bearing 110, such that the frictional forces between the cage bearing 110 and shaft 112 cause the force required to initiate relative movement thereof to be inconsistent. Moreover, the use of a contact sensor 122 may such give to problems with the contact sensor itself, such as contamination and wear. There is a desire to develop a bondhead that is lighter and more reliable as compared to the aforementioned conventional bondhead 100.